1. Field of the Invention
The present invention relates to a sensor apparatus using a metallic fine periodic structure and used for monitoring, by utilizing surface plasmon resonance (SPR), environmental changes accompanied with changes in dielectric response in the vicinity of a surface or changes in a surface condition due to antigen-antibody reaction or the like.
2. Description of the Related Art
Sensors utilizing surface plasmon resonance utilize surface plasmon polaritons (SPPs) existing at an interface between a metal and a dielectric.
SPPs at a flat plane interface have an electric field distribution in a space of several hundred nanometers in the vicinity of the surface. Therefore a sensor using SPPs finds application as a refractive index sensor sensitive in the vicinity of a surface.
In ordinary cases, there is a need to achieve phase alignment between incident light and SPPs for excitation of SPPs, and an oblique incidence construction through a prism, e.g., one using a Kretchmann configuration is adopted.
On the other hand, a unit in which a periodic fine structure formed of a metal is provided on the above-described interface instead of a metallic flat surface to achieve phase alignment between incident light and SPPs is also known widely (Japanese Patent Application Laid-Open No. 2005-257458).
Plasmon sensors using a conventional metallic fine periodic structure utilize a construction for observing a change in plasmon resonance spectrum as a sensor response and have such a characteristic that the resonance wavelength and sensitivity in such a case depend largely on the incident angle. Advantageously, this means that the resonance wavelength can be optimized by adjusting the incident angle in a case where a small-line-width light source such as a laser is used. On the other hand, the sensitivity is limited by diffraction of incident light itself unless a sufficiently-collimated large beam is used. There is, therefore, a problem that the degree of freedom with which a measuring optical system is designed is low. There is also a problem that the response is sensitive to alignment errors.
It is, therefore, an object of the present invention is to provide a plasmon sensor apparatus using a metallic fine periodic structure and capable of reducing the dependence of the resonance wavelength and sensitivity on the incident angle, increasing the degree of freedom with which a measuring optical system is designed, and increasing an alignment tolerance margin.